1. Field of the Invention
The present invention relates to a marine drive, and in particular to a transmission for a marine drive.
2. Description of the Related Art
Many watercraft employ outboard motors that are mounted on the transom of the watercraft. An outboard motor generally includes a power head that houses an engine, a drive shaft housing situated below the power head, and a lower unit that is positioned below the drive shaft housing. The lower unit typically houses a transmission and a propulsion shaft that drives a propulsion device.
Some outboard motors employ counter-rotating propeller systems which utilize a pair of counter-rotating propellers which operate in series about a common rotational axis. By using propeller blades having a pitch of opposite hand, the dual propeller arrangement provides significant improvement in propulsion efficiency.
Some outboard motors now employ forward/neutral/reverse transmissions together with the dual counter-rotating propeller system. These transmissions typically include a driving bevel gear and a pair of oppositely rotating driven bevel gears. Each driven gear includes a hub that is journalled within a lower unit of the outboard motor. A front dog clutch of a dual clutch assembly is positioned on a front side of the front driven gear hub. The front clutch selectively engages corresponding teeth formed on the front side of the hub of the front gear to drive an inner propeller shaft. The inner propulsion shaft in turn drives a rear propeller.
The rear dog clutch of the clutch assembly is interposed between the pair of oppositely rotating gears. In this position, the rear dog clutch moves between positions in which the clutch engages one of the gears. In this manner, the rear dog clutch selectively couples an outer propeller shaft to one of the driven gears to rotate a front propeller in either a forward or a reverse direction.
An actuator moves the clutches in to and out of engagement with the driven gears. The clutches desirably move in unison and for that matter a shift operator interconnects the clutches. In one prior transmission, the shift operator is formed by a plunger rod that is coupled to each clutch by a connecting pin. The front connecting pin directly connects the front clutch to the plunger such that the plunger and the front clutch rotate together. The plunger, however, is not so directly connected to the rear clutch. A coupling connects the plunger to the rear clutch in a manner that allows the rear clutch to rotate in a counter direction from the rotational direction of the plunger.
The coupling in some prior transmissions includes an annular bushing that is captured within a counterbore of the rear clutch. The annular bushing is supported therein to permit the annular bushing to rotate in an opposite direction from that of the counter-rotating rear dog clutch. The ends of the pin are embedded within the annular bushing with the annular bushing interposed between a pair of washers within the counterbore. The axial movement of the plunger moves the pin and the annular bushing, and thus the rear dog clutch.